Elizabeth McGovern as Mrs. Conway in “Time and the Conways.”Jeremy Daniel

Elizabeth McGovern spent six years playing the ideal mother — the warm, wise and nurturing Lady Cora of “Downton Abbey.” Clearly, she was ready for a change, and now she’s found one.

As the matriarch in Broadway’s “Time and the Conways,” opening Oct. 10, McGovern gives us the “anti-Cora”: a childish, narcissistic British matriarch who, between world wars, manages to ruin the lives of all six of her children.

No wonder that role in this 1937 J.B. Priestley play appealed to her.

“Cora is in many ways the perfect mother, and Mrs. Conway, the least perfect you could possibly imagine,” McGovern tells The Post. “In spite of all her best intentions and love, her instincts are almost 100 percent wrong! She wants great things for her children, but she makes the mistake that parents very often do: projecting their own ideal image of what they want their child to be instead of accepting them and loving them for who they are.”

The 56-year-old has given parenting some thought, having two daughters of her own. “They’re grown, thank God, so whatever damage done has already been inflicted,” she says, laughing. “I’m not … molding and shaping them like blocks of clay anymore!”

Offstage, McGovern’s accent wavers between that of her native Midwest and her adopted London, though not in an affected, Madonna-y way. She went to high school in California, where her father taught law at UCLA, and moved to New York to study at Juilliard, taking leave to play Timothy Hutton’s girlfriend in “Ordinary People.”

After that came “Ragtime,” “Once Upon a Time in America” and in 1990, the pre-Elisabeth Moss version of Margaret Atwood’s “The Handmaid’s Tale.” (McGovern says she’s yet to find time to watch the Emmy-winning miniseries.)

She moved to London 24 years ago, after marrying British filmmaker Simon Curtis (“My Weekend With Marilyn”). It wasn’t an easy adjustment.

“It’s a very different culture, even though we speak the same language,” she says. “It’s actually quite a wonderful place to live in now. You’re very close to everything — all of English government, culture, music.”

Even with a British husband and London-schooled children, she says it helped to have a dialect coach on standby for “Time and the Conways,” because, she says, “it’s good to have a third ear!”

Better still is having a fight director like Thomas Schall, who choreographed the slap Mrs. Conway gives her son-in-law, played by Steven Boyer. It’s a moment that makes the audience gasp.

“That’s an actual full-on smack that I give him,” McGovern says. “We practice it every day before the show. Steven has to present [his] cheek in just the right way … He’s a good sport, though!”

McGovern misses the people of “Downton Abbey,” but was quite ready to move on.
“Six years was enough for me,” she says. “I feel like we told every story there was to tell with those characters. Nothing good goes on forever.”

Once “Time and the Conways” ends its run on Nov. 26, she’s hoping for “a nice big rest.”

“I’m very good about detaching myself,” says McGovern, whose London band, Sadie and the Hotheads, is about to release its fourth album. (Michelle Dockery, McGovern’s “Downton” daughter Mary, performed on their second.)

“Once the work is done, I let it go,” she says. “It’s going to have its own life, and it’s really not my area of control.”